1. Field of the Invention
The present invention relates to a piezoelectric micro-blower arranged to convey compressible fluid, such as air.
2. Description of the Related Art
A piezoelectric micro-blower is known as an air blower for effectively dissipating heat generated in a housing of a portable electronic apparatus or for supplying oxygen required to generate electric power in a fuel cell. The piezoelectric micro-blower is a type of pump that includes a diaphragm that bends when a voltage is applied to a piezoelectric element, and is advantageous in that the piezoelectric micro-blower has a simple structure, small size and thickness, and low power consumption.
Japanese Examined Patent Application Publication No. 64-2793 discloses a flow-generating apparatus including a base member that includes a compression chamber filled with fluid, a nozzle plate including a nozzle that faces the compression chamber, and a vibrator including an opening and attached to the nozzle plate such that the nozzle is arranged at substantially the center of the opening. The nozzle plate and the vibrator are attached to the base member, and an alternating signal with a frequency close to a resonance frequency of the vibrator is supplied to the vibrator. In this case, no check valve is required and a flow rate can be increased by driving the vibrator at a high frequency. FIG. 5 of Japanese Examined Patent Application Publication No. 64-2793 illustrates a structure in which an inflow air chamber is provided in front of the nozzle plate and airflow ejected from the nozzle is discharged through an outlet together with the air surrounding the airflow in the air chamber.
Japanese Unexamined Patent Application Publication No. 2005-113918 discloses a micro-blower including an ejection unit that sucks in outside air and ejects the air, a cover unit in which an outlet arranged to discharge the air ejected from the ejection unit is provided, and a base unit bonded to the ejection unit. Referring to FIG. 4 of Japanese Unexamined Patent Application Publication No. 2005-113918, an ejection plate including suction holes and an ejection hole is provided, and a vibrating plate provided with a magnetic sheet is attached to a back side of the ejection plate with a compression chamber provided therebetween. The magnetic sheet is vibrated by a coil, so that airflow is ejected through a cavity. The airflow is discharged through the outlet together with air in a cover cavity that is arranged in front of the ejection plate.
Japanese Unexamined Patent Application Publication No. 2006-522896 discloses a gas flow generator including an ultrasonic driver in which a piezoelectric element is bonded to a stainless-steel disc at one side thereof, a first stainless-steel membrane fixed to the stainless-steel disc at the other side thereof, and a second stainless-steel membrane mounted such that a hollow space is provided between the first and second stainless-steel membranes.
High energy efficiency is one of the properties required of micro-blowers. In other words, it is necessary to keep energy loss as low as possible when converting input electrical energy into air ejection flow rate. In Japanese Examined Patent Application Publication No. 64-2793, since a double-wall structure including an inner case and an outer case is provided, vibration of the inner case does not easily leak to the outside. However, since a wall portion that connects the inner case and the outer case to each other is rigid and, in particular, since the wall portion extends in a vibrating direction of the vibrator, vibration of the vibrator is easily transmitted from the inner case to the outer case through the wall portion. The outer case is fixed to, for example, a housing or a substrate of an apparatus. When the vibration of the vibrator leaks to the outer case, there is a problem in that the energy loss increases and the characteristics vary in accordance with a fixing structure arranged to fix the outer case to the housing.
In Japanese Unexamined Patent Application Publication No. 2005-113918, the vibrator is attached to the ejection plate with a reservoir body provided therebetween, and an outer peripheral portion of the ejection plate is fixed to an outer case. The ejection plate is a relatively thick plate that does not vibrate in response to the vibration of the vibrator. Therefore, the vibration of the vibrator is transmitted to the outer case, which increases the energy loss as in Japanese Examined Patent Application Publication No. 64-2793.
In Japanese Unexamined Patent Application Publication No. 2006-522896, the second stainless-steel membrane is fixed to a housing. Since the first stainless-steel membrane and the second stainless-steel membrane are fixed at outer peripheral portions thereof, vibration of the ultrasonic driver directly leaks to the outside. Therefore, it can be assumed that the energy loss is greater than those in Japanese Examined Patent Application Publication No. 64-2793 and Japanese Unexamined Patent Application Publication No. 2005-113918. In addition, there is a possibility that the characteristics will vary in accordance with a fixing structure arranged to fix the second stainless-steel membrane to the housing.